Interpretive Summary: Selenium is an essential micronutrient for animal and human nutrition. Because of large areas of soil that contains low levels of selenium and consequently low levels of selenium supply in food, selenium deficiency is a widespread problem. Thus, increasing selenium content in food crops can have a positive impact on reducing selenium deficiency in the world. Exploiting genotypic variation is likely to be an effective method for selenium biofortification in crops. Lettuce is one of the most consumed leaf vegetables in many parts of the world. By examination of diverse lettuce accessions, we found genotypic variation of lettuce germplasm upon selenate and selenite treatment in terms of selenium accumulation as well as plant growth, total antioxidant levels, and amino acid contents. Our research will be helpful in selecting and developing better cultivars with relatively higher ability to accumulate Se and better nutritional qualities. This information will be of help for selenium biofortification programs using lettuce, which could have immediate impact on providing substantial levels of selenium for daily requirement.

Technical Abstract:
Selenium (Se) is an essential micronutrient for animals and humans. Increasing Se content in food crops offers an effective approach to reduce the widespread selenium deficiency problem in many parts of the world. In this study, we evaluated thirty diverse accessions of lettuce (Lactuca sativa L.) for their capacity to accumulate Se and their responses to different forms of Se in terms of plant growth, nutritional characteristics, and gene expression. Lettuce accessions responded differently to selenate and selenite treatment, and selenate is superior to selenite in inducing total Se accumulation. At least over 2-fold change in total Se levels between cultivars with high and low Se content was found. Synergistic relationship between Se and sulfur accumulation was observed in nearly all accessions at the selenate dosage applied. The change of shoot biomass varied between lettuce accessions and the forms of Se used. The growth-stimulated effect by selenate and the growth-inhibited effect by selenite were found to be correlated with the alteration of antioxidant enzyme activities. The different ability of lettuce accessions to accumulate Se following selenate treatment appeared to be associated with an altered expression of genes involved in Se/S uptake and assimilation. Our results provide important information for the effects of different forms of Se on plant growth and metabolism. They will also be of help in selecting and developing better cultivars for Se biofortification in lettuce.